The present invention relates to a battery pack and charging stand for charging the battery pack. More specifically, this invention relates to a battery pack and charging stand for charging the battery pack without electrical contacts for battery charging whereby electrical power is transmitted by the action of electromagnetic induction caused by locating a primary coil and a secondary coil in close proximity.
The battery pack can be charged when attached to a portable electrical device by, for example, charging terminals exposed from the bottom surface of the attached battery pack. On the other hand, discharging terminals of the battery pack, which serve to connect the battery pack and the portable electrical device, are internal to the portable electrical device with the battery pack attached. However, when the portable electrical device is attached to a charging stand, the charging terminals must make electrical contact with the supply terminals on the charging stand. Therefore, it is necessary to position the charging terminals where they will always be exposed. Especially, the battery pack, which is attached to the portable electrical device which mounts on the charging stand, requires the charging terminals to be in a position where they will be exposed outside even in the condition where it is attached to portable electrical device. For this reason, the charging terminals of the battery pack can be exposed to extremely dirty environments, and this system has the disadvantage that electrical contact problems can easily occur when attached to the charging stand.
In particular, for charging stands to discriminate between battery pack types and optimize charging conditions, multiple charging terminals have become common. It is difficult to attach a multiple charging terminal battery pack to a charging stand without developing contact problems on any of the charging terminals. Detrimental effects such as degraded rechargeable battery performance can occur due to charging without good contact at all of the charging terminals. For example, if the type of rechargeable battery contained in the battery pack is mistaken and charging is performed with large currents, or if charging is performed without correct battery temperature readings, degradation of battery performance can occur.
As noted, battery pack charging terminals are exposed when the known battery pack is connected to the portable electrical device. Therefore, when the portable electrical device is transported in a pocket or a carrying bag, problems such as short circuits can develop due to contact with the charging terminals and metallic objects or chains, which are also transported in the pocket or bag.
To solve these problems, a battery pack, which attaches to the portable electrical device and has rechargeable batteries that are charged by electrical power supplied from the portable electrical device without using exposed contacts, has been developed. This type of the battery pack is not directly charged by the charging stand but rather is charged via the portable electrical device. The portable electrical device comprises a secondary coil housed therein and the charging stand comprises a primary coil which is electromagnetically coupled with the secondary coil. Electrical power is transmitted by electromagnetic induction from the primary coil of the charging stand to the secondary coil of the portable electrical device. The portable electrical device rectifies the alternating current (AC) induced in the secondary coil and converts it into direct current (DC). This DC power is controlled by a control circuit and supplied to the battery pack to charge the rechargeable batteries. The battery pack and portable electrical device are connected by charge-discharge terminals. The portable electrical device is attached to the charging stand when charging the battery pack. In this condition, electrical power is supplied from the primary coil of the charging stand to the secondary coil of the portable electrical device, and the output of the secondary coil is controlled by the control circuit. Then electrical power is supplied from the portable electrical device to the battery pack. When the portable electrical device is detached from the charging stand, electrical power is then supplied from the battery pack to the portable electrical device and the portable electrical device can be used.
According to this method, the battery pack charged by the portable electrical device does not need to have exposed charging terminals, nor does it require the portable electrical device to be connected to the charging stand via contact points in the condition in which the battery pack is attached to the portable electrical device. Therefore, this type of battery pack has the advantage that the portable electrical device is attached to the charging stand and the battery pack can be charged without any contacts. However, the battery pack cannot be charged when it is detached from the portable electrical device. For this reason, there is a disadvantage in that any spare battery pack cannot be attached to and charged by the charging stand while the portable electrical device is in use.
Further, the battery pack with this structure may be connected to and charged by the portable electrical device via control signal terminals, in addition to charge-discharge terminals such as positive or negative terminals. This battery pack cannot be charged correctly if the electrical contact of the control signal terminals are poor. In this case, charging will not be achieved safely or may charge the batteries in a manner which results in significant battery degradation. This is because a charging circuit housed in the portable electrical device cannot correctly determine the type or condition of the battery pack during charging.
Furthermore, the method of charging the battery pack by transmitting electrical power from the charging stand to the portable electrical device by electromagnetic induction may pose another problem in that it is difficult to position the secondary coil in an appropriate position within the portable electrical device. It especially gets difficult for the portable electrical device, which has the battery pack at its back, to position the secondary coil in the appropriate position. This is because the bottom part of the case of the portable electrical device is very thin where it is appropriate to position the secondary coil.